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PDF LM2576S-XX Data sheet ( Hoja de datos )
| Número de pieza | LM2576S-XX | |
| Descripción | 3A Step-Down Voltage Regulator | |
| Fabricantes | ETC | |
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LM2576
3A Step-Down Voltage Regulator
GENERAL DESCRIPTION
The LM2576 Series are step-down switching
regulators with all required active functions. It is
capable of driving 3A load with excellent line and
load regulations. These devices are available in
fixed output voltages of 3.3V, 5V, 12V and an
adjustable output version.
The LM2576 series offers a high-efficiency
replacement for popular three-terminal linear
regulators. Also it requires a minimum number of
external components. It substantially not only
reduces the area of board size but also the size of
heat sink, and in some cases no heat sink is
required. The ±4% tolerance on output voltage
within specified input voltages and output load
conditions is guaranteed. Also, the oscillator
frequency accuracy is within ±10%. External
shutdown is included. Featuring 80µA (typical)
standby current. The output switch includes
cycle-by-cycle current limiting, as well as thermal
shutdown for full protection under fault conditions.
This series are offered in 5-pin TO-263,
TO-220 package.
Block Diagram
FEATURES
Guaranteed 3A output current.
3.3V, 5V, 12Vand adjustable versions,
Wide input voltage range, up to 45V
Internal oscillator of 52KHz fixed frequency.
Wide adjust version output voltage range,
from 1.23V to 37V ±4% max. at over line and
load conditions.
Low standby current, typ. 80µA, at shutdown
mode
Requires only 4 external components
Thermal shutdown and current limit
protection
P+ product enhancement tested
APPLICATIONS
LCD Monitors.
ADD-ON Cards Switching Regulators
High Efficiency Step-Down Regulators
Efficient Pre-regulator for Linear Regulators
Positive to Negative converter (Buck-Boost)
DC Input
+
Vin
1
Internal
Regulator
Enable
Enable
5
4
Feed
Back
R2
+-
R1
1K
1.23V
Band-Gap
Reference
Fixed Gain
3Amp.
Error amp. Comparator Driver Switch
+-
Thermal
Shutdown
52KHz
Oscillator
Reset
Current
Limited
Output
2
3
L1
+
Cout
D1
Ver1.0
1
1 page  
OB2269
Application Information
It is required that VIN must be bypassed with at
least a 100µF electrolytic capacitor for stability.
Also, it is strongly recommended the capacitor’s
leads must be dept short, and located near the
regulator as possible.
For low operating temperature range, for example,
below -25℃, the input capacitor value may need
to be larger. This is due to the reason that the
capacitance value of electrolytic capacitors
decreases and the ESR increases with
lower temperatures and ago. Paralleling a
ceramic or solid tantalum capacitor will
increase the regulator stability at cold
temperatures.
Output Capacitor
An output capacitor is also required to filter
the output voltage and is needed for loop
stability. The capacitor should be located
near the LM2576 using short PC board traces.
Low ESR types capacitors are recommended for
low output ripple voltage and good stability.
Generally, low value or low voltage (less than12V)
electrolytic capacitors usually have higher ESR
numbers, For example, the lower capacitor
values (220µF - 1000µF) will yield typically 50mV
to 150mV of output ripple voltage, while
larger-value capacitors will reduce the ripple to
approximately 20mV to 50mV.
The amount of output ripple voltage is primarily a
function of the ESR (Equivalent Series
Resistance) of the output capacitor and the
amplitude of the inductor ripple current (△IIND)
Output Ripple Voltage = ( △ IIND) x (ESR of
COUT) Some capacitors called “high-frequency”,
“low-inductance”, or “low-ESR” are recommended
to use to further reduce the output ripple voltage
to 10mV or 20mV. However, very low ESR
capacitors, such as tantalum capacitors, should
be carefully evaluated.
Catch Diode
This diode is required to return path for the
inductor current when the switch is off. It should
be located close to the LM2576 using short leads
Ver1.0
LM2576
and short printed circuit traces as possible.
To satisfy the need to fast switching speed and
low forward voltage drop, Schottky diodes are
widely used to provide the best efficiency,
especially in low output voltage switching
regulators (less than 5V). Beside, Fast-Recovery,
high-efficiency, or ultra fast recovery diodes are
also suitable. But some types with an abrupt
turn-off characteristic may cause instability and
EMI problems. A fast recovery diode with soft
recovery characteristics is better choice.
Inductor Selection
The LM2576 can be used for either continuous or
discontinuous modes of operation. Each mode
has distinctively different operating characteristics,
which can affect the regulator performance and
requirements.
With relatively heavy load currents, the circuit
operates in the continuous mode (inductor current
always flowing). But under light Load conditions,
the circuit will be force to the discontinuous mode
(inductor current falls to zero for a period of time).
For light loads (less than approximately 300mA) it
may be desirable to operate the regulator in the
discontinuous mode, primarily because of the
lower inductor values required for the
discontinuous mode.
Indictors are available in different styles such as
pot core, toroid, E-frame, bobbin core, et., as well
as different core materials such as ferrites and
powdered iron. The least expensive, the bobbin
core type, consists of wire wrapped on a ferrite
rod core. This type of construction makes for an
inexpensive inductor, but since the magnetic flux
is not completely contained within the core, it
generates more electromagnetic interference
(EMI). This EMI can cause problems in sensitive
circuits, or can give incorrect scope readings
because of induced voltage in the scope probe.
An inductor should not be operated beyond its
maximum rated current because it may saturate.
When an inductor begins to saturate, the
inductance decreases rapidly and the inductor
begins to look mainly resistive (the DC resistance
5
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| PDF Descargar | [ Datasheet LM2576S-XX.PDF ] | |
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